This invention relates to an organic light-emitting device (hereinafter abbreviated as OLED), particularly the device can be used preferably as an optical resonator type organic electroluminescence device with high directionality in light output.
Optical resonator type OLEDs are characterized by high directionality showing sharp light emission spectra and are expected to be promising in applications such as liquid crystal projectors, optical telecommunications devices, and exposure sources for printers. Aiming at improved directionality, JP-A-9-180883 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) proposes an OLED comprising a pair of dielectric multilayer reflectors making up a resonator and having an active layer sandwiched therebetween, wherein the resonance wavelength is set in the shorter wavelength than the peak wavelength of the electroluminescence (EL) spectrum thereby to suppress light emitted in directions other than the vertical to the substrate. However, as long as there exists an emission spectrum in the wavelengths shorter than the resonance wavelength, it necessarily follows that shorter wavelength light is emitted with an angle, causing reduction in directionality or emission of light other than the vertical resonance wavelength.
An object of the present invention is to provide a highly directional OLED.
The object of the present invention is accomplished by:
(1) An organic light-emitting device (OLED) comprising a substrate, a first reflective mirror, a transparent electrode, an organic light-emitting layer (OLE layer), and a back electrode in this order, which has on the reverse of the substrate a second reflective mirror having R1 (xcex8=0xc2x0) of 80 to 100% and R2 (xcex8=0xc2x0) of 0 to 40%, wherein R1 (xcex8) is an average reflectance at a wavelength xcex being 400 nm to (xcex0xe2x88x92xcex94xcex) (where xcex0 is a resonance wavelength; and xcex94xcex=xcexmaxxe2x88x92xcex0, xcexmax is a maximum wavelength that is obtained by measuring reflectance having the same value equal to Rxcex1 in a wavelength range about 400-700 nm. Rxcex1 is an average reflectance at a wavelength range from 400 nm to (xcex0xe2x88x92100) nm.) at an incidence angle xcex8, and R2(xcex8) is an average reflectance at a wavelength xcex is xcex0 to 700 nm at an incidence angle xcex8; and
(2) An organic light-emitting device comprising a substrate, a first reflective mirror, a transparent electrode, an OLE layer, and a back electrode in this order, which has on the reverse of the substrate a second reflective mirror having dxcex(xcex8)/dxcex8 having an absolute value of 10 or smaller, wherein xcex(xcex8) is a wavelength giving a reflectance (R1(xcex8)+R2(xcex8))/2; and R1(xcex8) and R2 (xcex8) are as defined above.
The OLEDs of the present invention include the following preferred embodiments.
(3) An OLED according to (2) above, wherein the second reflective mirror has R1(xcex8=0xc2x0) of 80 to 100% and R2(xcex8=0xc2x0) of 0 to 40%.
(4) An OLED according to any one of (1) to (3) above, wherein the second reflective mirror is smaller in area than the first reflective mirror.
(5) An OLED according to anyone of (1) to (4) above, wherein the OLED further has third to (n+2)""th reflective mirrors having different reflection characteristics formed on the second reflective mirror.
(6) An OLED according to anyone of (1) to (5) above, wherein the substrate has a thickness of 5 xcexcm to 10 cm.
(7) An OLED according to anyone of (1) to (6) above, wherein at least one of the first and second reflective mirrors is a multilayer thin film.
(8) An OLED according to (5) above, wherein at least one of the third to (n+2)""th reflective mirrors is a multilayer thin film.
(9) An OLED according to (7) or (8) above, wherein a difference between the highest and the lowest of the refractive indices of materials fabricating the multilayer thin film is 1.0 or smaller.
(10) An OLED according to any one of (7) to (9) above, wherein the number of layers making up the multilayer thin film is 6 or greater.
(11) An OLED according to any one of (7) to (10) above, wherein the multilayer thin film is a dielectric multilayer thin film.
(12) An OLED according to any one of (7) to (11) above, wherein the multilayer thin film contains at least one of ZrO2, Al2O3, TiO2, SiO2, CeO2, CaF2, LiF, MgF2, Na3AlF6, CeF2, MgO, ThO2, SiO, Sb2O3, In2O3, ZnO, SnO2, HfO2, Ta2O5, ZnS, CdS, CdTe, ZnSe, Sb2S3, Si, CdSe, and Ge.
(13) An OLED according to any one of (7) to (12) above, wherein the multilayer thin film contains at least one of ZrO2, Al2O3, TiO2, and SiO2.
(14) An OLED according to any one of (7) to (13) above, wherein the multilayer thin film contains at least one of ZrO2 and Al2O3.
(15) An OLED according to any one of (7) to (14) above, wherein the multilayer thin film contains at least one transparent conductive layer.
(16) An OLED according to any one of (7) to (15) above, wherein the multilayer thin film contains at least one of In2O3, ZnO, and SnO2.